Vehicles today use, for example, urea as reductant in SCR (selective catalytic reduction) systems which comprise an SCR catalyst, in which catalyst said reductant and NOx gas can react and be converted to nitrogen gas and water. Various types of reductants may be used in SCR systems. AdBlue is an example of a commonly used reductant.
One type of SCR system comprises a container for a reductant. The SCR system may also have a pump adapted to drawing said reductant from the container via a suction hose and to supplying it via a pressure hose to a dosing unit situated adjacent to an exhaust system of the vehicle, e.g. adjacent to an exhaust pipe of the exhaust system. The dosing unit is adapted to injecting a necessary amount of reductant into the exhaust pipe upstream of the SCR catalyst according to operating routines stored in a control unit of the vehicle. To make it easier to regulate the pressure when no or only small amounts are being dosed, the system comprises also a return hose which runs back from a pressure side of the system to the container. This configuration makes it possible to cool the dosing unit by means of the reductant which, during cooling, flows from the container via the pump and the dosing unit and back to the container. The dosing unit is thus provided with active cooling.
In certain operating situations, the dosing unit cannot be cooled adequately. One such case may be where the reductant of the SCR system is wholly or partly frozen, with consequent adverse effects on a cooling flow of the dosing unit. Another such case may be where the reductant in the SCR system has been used up or the pump does not function as intended. A further such case may be where there is leakage of the SCR system. Such leakage might for example occur at a fastening between a hose and the pump. Alternatively, said leakage might occur on a hose of the SCR system.
The above operating situations involve risk of the dosing unit being degraded functionally, becoming overheated and sustaining permanent damage or even completely disintegrating. Even temperatures which are not critical for the hardware of the SCR system entail risk that the reductant might be adversely affected by the heat, which might result in crystallisation potentially leading to obstruction of, for example, the dosing unit.
There is thus a need to improve current SCR systems in order to reduce or eliminate the above disadvantages.
WO 2010003424 A1 describes a method and a system for dosing liquid in an exhaust line of a combustion engine.